在Qt中确定TCP套接字上的数据类型

Question

I am writing a program to send images captured from an OpenCV window over a TCP connection, using Qt libraries to setup the connections etc.

I have to functions (below) which are both working to send either text or a byte array. The problem I have is at the other end how can I tell if the data coming in is plain text, or an array containing an image. Is there an inbuilt way to do this, or do I need to put a byte at the start of the data to tell the receiver what data is coming? I already put the array length at the start of the serialized image data.

void Screenshot_controller::sendText(std::string textToSend)
{
    if(connectionMade)
    {
        std::string endLine = "\r\n";
        textToSend = textToSend + endLine;
        const char * textChar = textToSend.c_str();
        sendSocket->write(textChar);
        sendSocket->flush();
        qDebug() << "Text Sent from Server";
    }
}

void Screenshot_controller::sendData(QByteArray dataToSend)
{
    if(connectionMade)
    {
        sendSocket->write(dataToSend);
        sendSocket->flush();
        qDebug() << "Data Sent from Server";
    }
}

Answer 1

You need to define the protocol yourself, whether that's with a byte, string, JSON header or any other method. The Tcp socket will allow you to transfer the data, but doesn't care what that data is; it's up to you to handle that.